Analysis of rankine cycle heat pump driers

We present a simulation analysis of closed Rankine cycle convective heat pump driers in which the product air recirculation ratin within the chamber is high. The configurations include driers with both external and internal refrigerant evaporators. The effects of modifications to basic designs are examined and real plant details are added in successive stages. Throughout the study the efficiency of each system is related to the second law loss mechanisms discussed by Carrington and Baines (1988). A detailed audit of exergy losses is presented for two driers in particular situations using data based on operational timber driers. The simulation results illustrate the need for the drier control strategy to take advantage of the performance characteristics of the heat pump drier. In addition, it is important to carefully match fans and heat exchangers to the drier requirements because the fan power will often be comparable with the compressor input.